This invention relates to a process and an apparatus for metal painting or spraying of articles.
There are plastic articles that require a painting with a metallic effect; however it is known that it is difficult to obtain such effect with the conventional paints, particularly when a strongly bright and reflecting surface, e.g. a mirrorlike surface, is desired.
As an example, many stage components or furnishings of shows and exhibitions, as well as many car prototypes advantageously can be realized of plastics or wood instead of uniformly In fact, plastics or wood, due to their light weight, easiness of transport and low cost which features are quite relevant for use in stage setting or due to their better workability in respect of metals, are materials quite convenient in making industrial patterns. It is of particular interest the construction of such patterns in plastic foam in view of the light weight, the availability and the low cost of this material.
The acceptance of these materials is however limited by the difficulties to impart to the articles a surface finish conferring them a satisfying matallized appearance, or that of other noble materials, such as marble or granite.
In the field of painting very small objects, such as plastic car models and the like, it is known a metallic painting process providing for the formation of a metal silver mirror, similarly to the technique employed in mirror manufacturing, in which an ammoniacal solution of silver nitrate is reduced with a solution of formic aldehyde or other organic reducing agent such as glucose, thus obtaining a thin reflecting film of metal silver imparting the desired appearance to the object.
These techniques are not used however in forming films having a metallizing appearance over larger objects or complex shape three-dimensional objects wherein problems are encountered concerning the adhesion of the silver film to the object surface, the film uniformity and the time stability, leading to a deterioration of the article appearance.
As for what concerns the painting with metallic effect of metal articles, the conventional techniques of electro-painting or vacuum painting suffer from the limitation of not being usable for very large size objects, particularly since it is not possible to place such objects in the painting tanks.
The object of the present invention is therefore that of providing an effective process for painting with a metallizing effect, i.e. markedly bright-reflecting, both plastic and wood articles, even of large size and complex shape, particularly articles built from material usually difficult to be painted, such as polystyrene and other foam resins, polymethacrylates and resins filled with glass fibers.
Another object of the invention is that of providing an apparatus which allows to carry out the above process in a easy and optimum manner.